Campbell worked in London, Vienna and Prague, developing his neurological speciality.

In 1892, Campbell was awarded a doctorate by the University of Edinburgh for his thesis The Pathology of Alcoholic Insanity.

Campbell's longest post in the UK was the thirteen years he spent working at Rainhill Asylum, Liverpool.

Shortly after his return, Campbell married a childhood friend, Jenny Mackay, with whom he had two daughters.

Campbell enlisted in the Australian Imperial Force and served as Major in the army in Egypt during the First World War.